The taxonomy, biostratigraphy, distribution, paleoecology and phylogenetic systematics of Oligocene planktonic foraminifera are treated in an illustrated atlas format. One hundred and twenty-eight species are recognized, including three species of Catapsydrax, eight species of Globorotaloides, two species of Protentelloides, twelve species of Paragloborotalia, two species of Parasubbotina, three species of Globigerina, eight species of Globigerinella, two species of Quiltyella Coxall and Spezzaferri n. gen., four species of Ciperoella Olsson and Hemleben n. gen., fifteen species of Globoturborotalita, seven species of Globigerinoides, seven species of Trilobatus, nine species of Subbotina, sixteen species of Dentoglobigerina, one species of Globoquadrina, two species of Turborotalita, three species of Acarinina, two species of Pseudohastigerina, two species of Turborotalia, two species of Dipsidripella, two species of Globigerinita, four species of Tenuitella, four species of Chiloguembelina, two species of Jenkinsina, two species of Cassigerinella, and four species of Streptochilus.

Over 2000 scanning electron micrographs images, including the type specimens of more than 60 species are illustrated for the first time, providing fresh comprehension of the shell architecture and wall texture, particularly for species that were poorly illustrated when first described. The biostratigraphic occurrences and phylogenetic relationships of all species of Oligocene planktonic foraminifera are reviewed. Analysis of wall textures, based on well-preserved material (much of which is illustrated for the first time) provides the basis for the higher taxonomy. Accordingly, Oligocene normal perforate planktonic foraminifera are divided into the Families Globigerinidae, Truncorotaloididae, and Globanomalinidae. Oligocene microperforate species, are placed in the Families Globigerinitidae, Chiloguembelinidae, Guembelitriidae, and Cassigerinellidae.